For my dissertation I am designing and building a radio controlled vehicle to carry camera equipment for wildlife filming. To provide the chassis for the buggy I am using a Tamiya Pershing Tank (M26).

I need further information on the workings of the DMD Control Unit, and DMD Multi Function Unit, especially what signals are used to control them. Does anyone know how I could find this out or have documentation that can help?

Also I need to adapt the tank to make it as quiet as possible, and have started to look at ways to silence the gear box first. Are there any different types of gears that are available to use instead of the spur gears provided with the kit to do this? Or are there any other ways that you would suggest to do this?

Any suggestions and help will be gratefully received!

Many thanks

Need more info. Is this an automated bot, or just a remotely piloted vehicle(RPV)? If it's RPV, can't you just use the existing control setup, replacing the turret rotation/elevation with camera rotation/elevation?
If it's automated, where is the control system, onboard or remote? If remote, using the existing RC TX? Or something else (wifi, bluetooth, gprs, etc)?

W.r.t noise, I'm guessing that stealth would be more important than speed, so the first thing would be to replace the motors with much slower wind motors. This will reduce motor noise, as well as require fewer gearing stages to get to the required speed range. Belt drives are often quieter than gears, but more fussy in terms of alignment and tension. Gearbox covers, rubber motor/gearbox mounts to reduce noise conduction, and some noise insulation (foam/fiberglass matting) would help. Breakin all the gears and then lube them to get the quietest operation possible.

David

It will be a remotely operated vehicle. The kit does not come with RX, so I will have to buy one. I will be using the tanks features to pan and tilt the camera as you suggested, however I need to build the remote control unit in order to control these functions. The control signal I will be using is RF, but without knowing more about the DMD control units I will not know what signals to send it to make it perform each function. Any ideas?

I am aware of some of the techniques you suggest to make it quieter, but unfortunately my local model shops do not stock anything compatible to used to adapt this model. Would you recommend any supplier for me to try?

Thanks

So basically you'll just be driving it normally as a remote control vehicle. Why not just use a standard RC radio system? It would save you a *lot* of time and hassle, and allow you to spend more time on the "novel" aspects of your project such as video gear, sound reduction, camouflage, etc. The statement "The control signal I will be using is RF" suggests you may not have done a lot of research into how this should be done from an architecture perspective (digital, analog, packet-based, serial-stream, frequencies), let alone the details involved. The signaling spec between the RX and the DMD/MF isn't hard to explain (it's several standard servo signals). The signal between the TX and RX would be a standard RC signal with four channels. I have no idea what the signalling between DMD & MF is, but there's probably no reason to intercept it.
I'm just afraid you're trying to reinvent the wheel for no particularly good reason?

For the mechanical conversion, parts could be a bit tricky. Most online RC shops will have some parts (e.g. towerhobbies), but it would be hard to fit stuff without seeing them or having the detailed measurements (it doesn't help if a gear is labelled as the pinion for a specific model truck for instance). Another option would be stores like http://www.smallparts.com/ where you can buy gears (delrin would be nice and quiet), timing belts, pulleys, etc.
For the drivetrain upgrade, you're going to be limited by what tools and equipment you have available. If you have access to a metal shop with lathe, drill press and mill, you can build virtually whatever you can think of. If you can only build gearboxes out of sheet metal, you can probably do a decent bit. If you're limited to replacing motors and gears, I think you may be very limited. You probably won't be able to even find quieter nylon/delrin gears to match the metal Tamiya ones.

D.

I would love to concentrate on making a all singing all dancing platform, but unfortunately with all the other projects we have to complete I will be lucky to accomplish the basic commands (forwards, backwards, left, right etc) Also its a communications based project so I would get very little marks for a fancy box on wheels, but not being able to control it. The frequency of the RF will depend up on the university as they have funny rules about these things, and will be digital apart from that I haven't as yet researched into the fine details. As with everything to do with uni I need to provide documentation, do you know of a good website or book etc on servos so I would be able to reference the information in my report?

The tools I have access to at uni consists of a soldering iron, and er...some pliers may be. There are probably some metal workshops somewhere but not sure if I would be able to use them. I will have a look at the web link though and see what I can find to help. Even if I can't source the materials to implement the techniques, I can still put forward recommendations of how to make it quieter, so every little helps!

Thank you, this information is very useful.

Ah, so you're actually implementing a *communications control* system for the tank. That's the sort of information that's handy to have up front, so people know what you're actually trying to accomplish.

A servo signal is pretty simple. Google or http://www.rc-cam.com/servotst.htm will tell you just about all you need to know about the signal format.
A Pershing will expect four separate servo signals, possibly in sequence (e.g. the 2nd signal starts when the first ends). One controls speed, one controls steering, one controls turret rotation, and one controls turret elevation. There are also several additional functions which are triggered by adjusting the centering trim of a channel and then banging the stick all the way over (and hence getting slightly more than normal "travel"), such as gun firing and lights. These probably won't interest you. *But*, IIRC, the Pershing requires one of these "trim+stick" combinations to put the tank "into gear", otherwise it won't actually drive. This could make it a bit trickier to implement, but doable. Note that the calibration of the DMD/MF may be an issue to be careful of.

Basically, you'll need either an existing multi-channel radio, or a radio signal processed by a micro-processor/controller to do this. If I were building a radio system (which I have), I'd use a digital FM signal in either 868/900 mhz or 2.4ghz, using a PIC or AVR to encode the signal on the TX, and also to decode on the RX. If you already knew anything about PICs/AVRs and had a radio in a "black box", you could probably churn out a simple system in a weekend of coding and wiring.

I would also strongly recommend that you buy/borrow an RC radio for testing. It would be very annoying to try and determine if the problem is bad wiring/electronics or your control system without one.

Good luck,
David

Unfortunately I'm not exactly an expert when trying to explain things, and as you have probably guessed I have never had any experience with this type of thing before, but everyone has to start somewhere! If it gives you a better idea of what I have to work with, the remote control unit will be using a Motorola GP32 as its brain controlled by a key pad of buttons. I have been told to write a programme using joysticks would be far too complicated in the time I have. []

If you have anymore words of wisdom or food for thought, I would be very grateful.

Thanks for all your time and help

Never used one, though did do some assembly on the 68HC11 in university. Are you using one on each end of your radio link?
Do you have enough control to be able to change the output state of pins (high, low) whenever you want? Or are you limited to outputing RS-232 or some such nonsense?
Buttons or joysticks shouldn't matter, it will just limit the granularity of commands you can send. The only issue might be calibrating the DMD/MF unit, but you could do that with a real RC radio first, then hookup your system.

Btw, an oscilloscope (and knowing how to basically use it) will be worth it's weight in gold on a project like this...

My first thought would be to get hold of an RC servo, and write a program on your GP32 to output a servo signal, and have it change (e.g. left -> right) when you press a button. Then have the servo signal set to neutral and have two positions at the extremes when you press one of two buttons. Then have the GP32 output four independent servo signals at the same time using 8 buttons (you could unplug and replug the servo in the different channels to test them), then you're pretty much capable of hooking into the DMD/MF unit.
If you get that far, move the button reading to the remote GP32 and add in the radio link. You'd really only need to transmit at most two/three bytes of data if you're just sending around 8 button positions.

D.

do remember that the pershing DMD has a 'lock' on its power until you do a full reverse trim and full reverse on teh throttle everytime you turn the master switch on, this puts teh tank 'in gear' and allows it to move after that. The instructions in the kit will state so. Some ppl over look that and wonder why their pershings do not move.

This reminds me of the documentary I saw where they used a camera mounted on a tiger chassis to go into burrows that pythons use to hide in the day.

[size=3]Hi

I've set up the tank as per instructions, and as you say, do a full reverse put put the tank in gear when I switch it on. However it will not move forward or backwards. It will only jump forward half a centimeter and stop. I only seem to be able to turn the lights on and off, rotate the turret and tilt the gun, which is all very impressive considering never done anything like this before, but entirely helpful.

Do you know what I am doing wrong or know anywhere I may be able to find a solution?


Also can you remember what the documentary was called about the pythons? Would be really useful to find some information on it so I can include it in my file.

Many thanks

Do you know that the tank works correctly without your controller? I.e. have you tried it with a regular RC controller to make sure that the motor & DMD<->MF hookup is correct.

After that's been verified, my thought would be that either your extreme values (i.e. full throw plus full trim equivalent) are not sufficient, or that the channel directions need to be reversed.

D.

I have no access to any other RC toys so just trying to make it work with a Futaba 4 channel transmitter and receiver.

If that helps?

Does it drive normally with the 4 channel Futaba TX/RX?

D.

Did you put teh trims back to center after you put teh tank 'ingear'

About the documentary, sadly I did not take note of teh show title as I was channel surfing and chance upon it on teh animal planet. Cannot seem to find anything about it online.

You not only have to move the throttle stick, but the throttle trim also. This is from the Tamiya MF-03 manual

As for noise keep in mind the electronics use PWM, which generates a high-pitched frequency whine.

While humans are not sensitive to this sound, this noise may scare animals in close proximity as their hearing range generally extends beyond ours.

Going with a straight analog ESC circuit would eliminate this.

Nope this is what I am having problems to get it to work normally as it should with the Futaba . I think I am putting it in gear OK, as it goes from a peaceful rumble to start to revving louder. Moving the controls and trims in any direction I get lots of impressive sounds but only ever a small hop forward, and only get this once in a while can't figure out what controls cause it.

HELP!!!

I don't know what I am doing wrong and no idea how to fix it.

Just out of curiosity, if stealth is a factor, why not consider a wheeled chassis? Plenty of R/C trucks out there that will offer as good or better cross country performance, and wheeled vehicles are always going to be quieter than tracked. Plus the setup will be easier, and less of a learning curve for driving.

Just a thought..


Andy

Did you calibrate it successfully with the trims in the neutral position?

D.

Thanks for the alternative idea. Can you give a few more details on what this type of circuit would involve please in being used to control the tank. Is it as easier to implement as using PWM?

I've reset the controls again and found that they are the opposite way around to what is stated on the website. I can now get it to go forwards and backwards, all be it in a wonky line! What is the easiest way to correct this? Are there any secretes in learning how to control it so it goes left and right gracefully?

Many thanks

If the controls seem backwards (push forward and tank goes backwards), your transmitter should have a set of switches for "servo reversing". You need to reverse the correct channel to get the controls to match what you're expecting.

If the controls appear to control the wrong functions (e.g. the throttle channel controls the turret), it's probably because the channels are plugged in "wrong". Depending on your radio, it may have different channel to stick assignments. (Mode 2 vs Mode 1). Swap the channels around until you get what you expect.

D.

Hi

I've been trying different channels swapped around and resetting the DMD etc, but can't seem to get it right so happy the way it is.

But what is extremely annoy is the high pitched tone when the motors are running, is there anyway to stop this by any chance?

And possibly more seriously regardless of if the switch on the tank is 'on' or 'off' the tank can still be moved! Can this be also fixed?

Thanks for all your help

Not really. The speed control of the motors is done via pulse width modulation (PWM) by chopping the current. This consists of sending pulses of power, with varying duration (from very short or low speed, up to basically on all the time or full power). The frequency of these pulses is what causes the high pitched whine. An ESC can use a different frequency of pulsing, which may make it less audible (to human ears anyway) but it's hard to get rid of.
A speed control could vary the voltage, but that's not common as far as I know (save the old mechanical speed controllers that used to be the only alternative).

Not sure why your tank still drives when the switch is off. My Sherman doesn't (engine shuts off) and it's done.

D.

I think the high pitch tone he might be refering to is that of the MF capacitor that is used to charge the flash unit. It has teh same sound a camera flash makes when its being charged or already charged. Btw do you have any use of the rest of teh pershing parts i.e the jerry cans the plastic machine gun, the turret and all its components like teh turret elevation unit barrel and flash unit. Was wonndering if you wantto sell them.